This application is based upon and claims the benefit of priority of Japanese Patent Applications No. 2000-228846 filed on Jul. 28, 2000, No. 2000-230505 filed on Jul. 31, 2000 and No.2001-96008 filed on Mar. 29, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electromagnetic valve for controlling fluid flow amount, typically, applicable to a variable discharge high pressure pump for diesel engines so as to adjust fuel amount discharged from the pump.
2. Description of the Prior Art
JP-A-11-336638 discloses an electromagnetic valve 120 shown in FIG. 14, which is applied to a variable discharge high pressure pump for a diesel engine.
In the electromagnetic valve 120 shown in FIG. 14, a valve body 122 is slidably housed in a valve case so as to change a flow path area. An end of the valve body 122 on right side in FIG. 14 is press fitted to an armature 123. When a coil 124 is energized, the valve body 122 and the armature 123 move in a valve opening direction (in right direction in FIG. 14) against a biasing force of a spring 125. Further, the electromagnetic valve 120 has a first stator (housing) 126 and a second stator 127. According to the electromagnetic valve 120 mentioned above, a displacement position (lift amount) of the valve body 122 is controlled by an amount of current to be applied to the coil 124 so that the flow path area, through which fluid flows, is regulated.
The armature 123, which constitutes a part of a magnetic circuit, is made of soft magnetic material such as pure iron. It is necessary to process the valve body 122 made of high speed steel SKH 51 with quenching and tempering treatments for improving wear resistance and reducing frictional force. Conventionally, the armature 123 and the valve body 122 are formed in advance as separate parts and, then, integrated into one body by press fitting from standpoints that the quenching treatment adversely affects on magnetic characteristic of the armature 123 made of soft magnetic material and that required functions of the armature 123 and the valve body 122 are inherently different.
Further, the first stator 126, which constitutes a part of a magnetic circuit similar as the armature 123, is made of soft magnetic material such as electromagnetic stainless steel. It is necessary to process the valve case 121, which is made of, for example, chromemolybdenum steel SCM 15, with carbonized hardening treatment (hardening depth is about 0.5 mm) for improving wear resistance and reducing frictional force similarly as the valve body 122. The first stator 126 and the valve case 121 are formed as separate parts since the carbonized hardening treatment adversely affects on magnetic characteristic of the first stator 126 and required functions of the valve case 121 and the first stator 126 are inherently different.
As mentioned above, the conventional electromagnetic valve 120 has a lot of parts whose functions are different so that the manufacturing cost is higher.
Furthermore, the coil 124 is accommodated in a resin bobbin 108. The electromagnetic valve 120 is provided at an end thereof with a resin connector 109. Electric signals are input to and output from the electromagnetic valve 120 via the resin connector 109.
Recently, it is highly demanded in view of protecting earth environment, preserving resources and promoting recycling to separate a resin member such as the bobbin 108 from a metal member such as the first and second stators 126 and 127 when the car incorporating the electromagnetic valve 120 is scraped. However, as the first and second stators 126 and 127 surround the resin bobbin 108, it is troublesome and requires complicated works to dismount the bobbin 108 out of the electromagnetic valve 120.
To solve the problems mentioned above, it is an object of the present invention to provide a compact electromagnetic valve having a less number of components in which at least one of the components has a plurality of functions selected from valve case, valve body, armature and stator functions.
To achieve the above object, in the electromagnetic valve to be fixed to a base housing for controlling fluid flow in housing fluid passages provided in the base housing, a case member having a stator and a valve case is provided inside with a cylindrical hollow extending from the valve case to the stator. A coil member arranged around the case member on a side of the stator, and a cylindrical moving member having an armature and a valve body is housed in the cylindrical hollow so that the valve body is in slidable contact with the valve case for controlling the fluid flow. The valve body is moved axially when the coil member is energized to generate magnetic flux passing through the stator and the armature.
With the electromagnetic valve mentioned above, the case member has a feature that the valve case and at least a part of the stator are integrally formed into one body to constitute a composite valve case and/or the cylindrical moving member has a feature that the valve body and the armature are integrally formed into one body to constitute a composite valve body.
It is preferable to have a construction that, when the cylindrical moving member moves in the cylindrical follow relatively to the case member, an amount of the fluid flowing through inner fluid passages provided in the case member and the moving member is changed.
Preferably, the composite valve case and/or the composite valve body is made of soft magnetic material for assuring better magnetic characteristics and is provided at a surface thereof with a hardened layer formed by a surface treatment or a heat treatment for improving wear resistance and reducing frictional force. It is preferable that the hardened layer is provided at least at one of a surface of the composite valve case and a surface of the composite valve body which are in sliding contact with each other. It is preferable that the hardened layer is a layer, whose depth is several xcexcm, formed by soft nitride heat treatment.
Preferably, the stator is composed of a first stator, a magnetic flux restricting element and a second stator which are arranged in series in an axial direction of the case member so that the magnetic flux mainly passes from the first stator via the armature to the second stator, while bypassing the magnetic flux restricting element.
Further, it is preferable that the magnetic flux restricting element is a thin wall portion of the case member whose wall thickness is thinner than that of any of the first and second stators through which magnetic flux passes. The thin wall portion has, preferably, a tapered outer surface whose diameter is smaller toward the armature for improving magnetic characteristics.
It is another object of the present invention to provide an electromagnetic valve in which a coil member is easily separated from a valve case member constituted by a stator and valve case.
To achieve the another object, the case member is provided outside with a flange surface extending outward perpendicularly to an axis thereof. A coil member, which is arranged around the case member on a side of the stator, is urged toward and fixed to the flange surface by a detachable fixing member such as a bolt or clip.
It is preferable that the coil member is composed of a solenoid having a center hole into which the case member on a side of the stator is inserted and a housing disposed outside the solenoid. With this construction, the solenoid and the housing are urged toward and fixed to the flange surface or the base housing by the detachable fixing member in a state that the solenoid is sandwiched between the flange surface and the housing. This construction is preferable on classically collecting or recycling waste material.